U.S. patent number 5,895,171 [Application Number 08/793,693] was granted by the patent office on 1999-04-20 for process for heating an asphalt surface and apparatus therefor.
This patent grant is currently assigned to Martec Recycling Corporation. Invention is credited to Mostafa Joharifard, Patrick C. Wiley.
United States Patent |
5,895,171 |
Wiley , et al. |
April 20, 1999 |
Process for heating an asphalt surface and apparatus therefor
Abstract
A process for heating an asphalt surface and an apparatus
therefor. The process comprises the steps of: igniting in a burner
(30) a combustible mixture comprised of a fuel (50) and oxygen (60)
to produce a hot gas; and feeding the hot gas to an enclosure
having a radiative face (200) disposed above the asphalt surface
(280). The asphalt surface heating apparatus comprises a hot gas
producing burner (30) and an enclosure (25) comprising an inlet
(120) for receiving hot gas from the burner and a radiative face
(200) having a plurality of apertures. The apertures in the
radiative face are of a dimension such that the hot gas: (i) heats
the radiative face to provide radiation heat transfer to the
asphalt surface; and (ii) passes through the apertures to provide
convection heat transfer to the asphalt surface.
Inventors: |
Wiley; Patrick C. (Vancouver,
CA), Joharifard; Mostafa (West Vancouver,
CA) |
Assignee: |
Martec Recycling Corporation
(Vancouver, CA)
|
Family
ID: |
4154277 |
Appl.
No.: |
08/793,693 |
Filed: |
February 27, 1997 |
PCT
Filed: |
September 01, 1995 |
PCT No.: |
PCT/CA95/00505 |
371
Date: |
February 27, 1997 |
102(e)
Date: |
February 27, 1997 |
PCT
Pub. No.: |
WO96/07794 |
PCT
Pub. Date: |
March 14, 1996 |
Foreign Application Priority Data
Current U.S.
Class: |
404/77; 404/79;
404/95 |
Current CPC
Class: |
E01C
23/14 (20130101) |
Current International
Class: |
E01C
23/14 (20060101); E01C 23/00 (20060101); E01C
007/06 (); E01C 023/14 () |
Field of
Search: |
;404/77,79,95 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Will; Thomas B.
Assistant Examiner: Hartmann; Gary S.
Attorney, Agent or Firm: Evenson, McKeown, Edwards &
Lenahan, P.L.L.C.
Claims
What is claimed is:
1. A process for heating an asphalt surface comprising:
igniting in a burner a combustible mixture which comprises a fuel
and oxygen to produce a hot gas;
feeding the hot gas to an enclosure having a radiative face
disposed above the asphalt surface, the radiative face having a
plurality of apertures; and
selecting the dimension of the apertures such that the hot gas:
(i) heats the radiative face to provide radiation heat transfer to
the asphalt surface; and
(ii) passes through the apertures to provide convection heat
transfer to the asphalt surface, the radiation heat transfer being
from about 20% to about 80% of the total heat transfer, the
remainder being convection heat transfer.
2. The process defined in claim 1, wherein the radiation heat
transfer is from about 35% to about 65% of the total heat transfer,
the remainder being convection heat transfer.
3. The process defined in claim 1, comprising the further step of
disposing the enclosure above the asphalt surface at a distance of
from about 1 to about 6 inches.
4. The process defined in claim 1, wherein the enclosure comprises
a plurality of substantially adjacent tubes in a spaced
relationship to define a gap between each pair of adjacent tubes,
each of said tubes having the radiative face.
5. The process defined in claim 4, comprising the further step of
recycling a portion of the hot gas to the burner through the gap
between the adjacent tubes after the hot gas has passed through the
apertures in the enclosure.
6. The process defined in claim 5, comprising the further step of
selecting the size of the gap such that the velocity of the hot gas
being recycled is in the range of from about 20% to about 80% of
the velocity of the hot gas passing through the apertures in the
enclosure.
7. The process defined in claim 5, comprising the further step of
selecting the size of the gap such that the velocity of the hot gas
being recycled is in the range of from about 30% to about 70% of
the velocity of the hot gas passing through the apertures in the
enclosure.
8. The process defined in claim 1, wherein the fuel is diesel
fuel.
9. The process defined in claim 1, wherein the radiation heat
transfer and the convection heat transfer both emanate from a
single enclosure.
10. An asphalt surface heating apparatus comprising a hot gas
producing burner and an enclosure comprising an inlet for receiving
hot gas from the burner and a radiative face having a plurality of
apertures, the apertures having a dimension such that the hot
gas:
(i) heats the radiative face to provide radiation heat transfer to
the asphalt surface; and
(ii) passes through the apertures to provide convection heat
transfer to the asphalt surface, the radiation heat transfer being
from about 20% to about 80% of the total heat transfer, the
remainder being convection heat transfer.
11. The asphalt surface heating apparatus defined in claim 10,
wherein the radiation heat transfer is from about 35% to about 65%
of the total heat transfer, the remainder being convection heat
transfer.
12. The asphalt surface heating apparatus defined in claim 10,
further comprising means to dispose the enclosure above the asphalt
surface at a distance of from about 1 to about 6 inches.
13. The asphalt surface heating apparatus defined in claim 10,
wherein the enclosure comprises a plurality of substantially
adjacent tubes in a spaced relationship to define a gap between
each pair of adjacent tubes, each of said tubes having the
radiative face.
14. The asphalt surface heating apparatus defined in claim 13,
wherein the tubes have a substantially non-circular
cross-section.
15. The asphalt surface heating apparatus defined in claim 13,
wherein the tubes have a substantially rectangular
cross-section.
16. The asphalt surface heating apparatus defined in claim 10,
further comprising means to recycle a portion of the hot gas to the
burner after the hot gas has passed through the apertures in the
enclosure.
17. The asphalt surface heating apparatus defined in claim 16,
wherein the gap is of a size such that the velocity of the hot gas
being recycled is in the range of from about 20% to about 80% of
the velocity of the hot gas passing through the apertures in the
enclosure.
18. The asphalt surface heating apparatus defined in claim 16,
wherein the gap is of a size such that the velocity of the hot gas
being recycled is in the range of from about 30% to about 70% of
the velocity of the hot gas passing through the apertures in the
enclosure.
19. The asphalt surface heating apparatus defined in claim 10,
wherein a single enclosure provides the radiation heat transfer and
the convection heat transfer.
Description
TECHNICAL FIELD
The present invention relates to a process for heating an asphalt
surface and to apparatus therefor.
BACKGROUND ART
As used herein, the term asphalt also comprises macadam and tarmac.
Asphalt paved road surfaces typically comprise a mixture of asphalt
cement (typically a black, sticky, petrochemical binder) and an
aggregate comprising appropriately sized stones and/or gravel. The
asphalt concrete mixture is usually laid, compressed and smoothed
to provide an asphalt paved road surface.
Over time, an asphalt paved road surface can deteriorate as a
result of a number of factors. For example, seasonal temperature
fluctuations can cause the road surface to become brittle and/or
cracked. Erosion or compaction of the road bed beneath the road
surface may also result in cracking. Moreover, certain of the
chemical constituents incorporated in fresh asphalt are gradually
lost over time or their properties changed with time, further
contributing to brittleness and/or cracking of the road surface.
Where concentrated cracking occurs, pieces of pavement may become
dislodged. This dislodgement can create traffic hazards, and
accelerates the deterioration of adjacent pavement and highway
substructure. Even if cracking and the loss of pavement pieces do
not occur, the passage of traffic can polish the upper highway
surface, and such a surface can be slippery and dangerous. In
addition, traffic-caused wear can groove, trough, rut and crack a
highway surface. Under wet highway conditions, water can collect in
these imperfections and set up dangerous vehicle hydro-planing
phenomena. Collected water also contributes to the further
deterioration of the pavement.
Prior to about the 1970's, available methods for repairing old
asphalt-paved road surfaces included: spot treatments such as
patching or sealing, paving with new materials over top of the
original surface, and removal of some of the original surface and
replacement with new materials. Each of these methods had inherent
drawbacks and limitations.
Since about the early 1970's, with increasing raw material, oil and
energy costs, there has been a growing interest in trying to
recycle the original asphalt. The world's highways have come to be
recognized as a very significant renewable resource.
Early recycling techniques involved removing some of the original
surface and transporting it to a centralized, stationary recycling
plant where it would be mixed with new asphalt and/or rejuvenating
chemicals. The rejuvenated paving material would then be trucked
back to the work site and laid. These techniques had obvious
limitations in terms of delay, transportation costs and the
like.
Subsequently, technology was developed to recycle the old asphalt
at the worksite in the field. Some such processes involved heating
and are frequently referred to as "hot-in-place recycling"
(hereinafter referred to as HIPR).
This technology comprises many known processes and machines in the
prior art for recycling asphalt paved surfaces where the asphalt
has broken down. Generally, these processes and machines operate on
the premise of (i) heating the paved surface (typically by using
large banks of heaters) to facilitate softening or plasticization
of an exposed layer of the asphalt; (ii) mechanically breaking up
(typically using devices such as rotating, toothed grinders; screw
auger/mills; and rake-like scarifiers) the heated surface; (iii)
applying fresh asphalt or asphalt rejuvenant to the heated, broken
asphalt; (iv) distributing the mixture from (iii) over the road
surface; and (v) compacting or pressing the distributed mixture to
provide a recycled asphalt paved surface. In some cases, the
heated, broken material can be removed altogether from the road
surface, treated off the road surface and then returned to the
surface and pressed into finished position. Much of the prior art
relates to variations of some kind on this premise.
Over time, HIPR has had to address certain problems, some of which
still exist today. For example, asphalt concrete (especially the
asphalt cement within it) is susceptible to damage from heat. Thus,
the road surface has to be heated to the point where it was
sufficiently softened for practical rupturing, but not to the point
of harming it, Furthermore, it was recognized that asphalt concrete
is increasingly hard to heat as the depth of the layer being heated
increases.
Many patents have attempted to address these problems. See, for
example, the following patents, each of which is incorporated
herein by reference:
U.S. Pat. No. 3,361,042 (Cutler) U.S. Pat. No. 3,970,404
(Benedetti)
U.S. Pat. No. 3,843,274 (Gutman et al.) U.S. Pat. No. 3,989,401
(Moench)
U.S. Pat. No. 4,011,023 (Cutler) U.S. Pat. No. 4,124,325
(Cutler)
U.S. Pat. No. 4,129,398 (Schoelkopf) U.S. Pat. No. 4,335,975
(Schoelkopf)
U.S. Pat. No. 4,226,552 (Moench) U.S. Pat. No. 4,534,674
(Cutler)
U.S. Pat. No. 4,545,700 (Yates) U.S. Pat. No. 4,711,600 (Yates)
U.S. Pat. No. 4,784,518 (Cutler) U.S. Pat. No. 4,793,730
(Butch)
U.S. Pat. No. 4,850,740 (Wiley) U.S. Pat. No. 4,929,120 (Wiley et
al.)
Regardless of the specific technique used, commercially successful
asphalt surface recycling is largely dependent on the ability to
heat the old asphalt surface to be recycled in an efficient manner.
Generally, efficient heating is achieved when the asphalt surface
is heated to the desired temperature (eg. 300.degree. F.) both
quickly and without substantial scorching or overheating.
It is conventional in the art to utilize a heater to soften the
asphalt thereby facilitating recycling thereof. The heater may be a
radiant heater (e.g. infrared heater), a hot air heater, a
convection heater, a microwave heater, a direct flame heater and
the like.
By far the most popular commercially utilized heater is a radiant
heater emitting infrared radiation. Generally, such a heater
operates by igniting a fuel/air mixture over a metal (or other
suitable material) screen resulting in combustion of the mixture.
The heat of combustion is absorbed by the metal screen which, in
most cases, results the metal screen glowing red and radiating the
asphalt surface with heat (i.e. infrared radiation). One of the
significant limitations of conventional radiant heaters is the
source of fuel. Specifically, since the fuel/air mixture must be
combusted of the entire radiative surface of the heater, the fuel
must be of a nature which enables it to be readily mixed with air
and distributed substantially evenly over the radiative surface up
to the point of ignition. The result of this is that virtually all
commercially available radiation heaters are fuelled by propane or
butane. Propane and butane are gases which may be readily mixed
with air for use in this application.
Unfortunately, propane and butane are very hazardous materials to
handle and use since they are typically stored under pressure which
can lead to a dangerous explosion in the event of an accidental
spark. Further, there are a number of countries in the world in
which propane and/or butane are: (i) unavailable, (ii)
prohibitively expensive, and/or (iii) unattractive in the face of
other available lower cost liquid fuels such as diesel fuel.
Indeed, one or more of these problems exist in most countries in
the world outside North America, Europe and Australia. With regard
to (iii), liquid fuels (i.e. fuels which are liquid at ambient
temperature and pressure) are unsuitable for use in conventional
radiation heaters due to the difficulties associated with atomizing
such fuels in air and distributing the fuel/mixture substantially
evenly over the radiative surface of the heater. The net result of
this is that HIPR is commercially impractical in most countries in
the world outside North America and Europe.
Further, with conventional radiation heaters, the temperature of
the radiative surface can easily reach 2000.degree. F. or more.
This results from the need to heat the surface as quickly as
possible so that the progression of all vehicles associated with
the recycling system is not delayed. This, coupled with the need to
heat the surface of the asphalt to a temperature of 300.degree. to
400.degree. F. with the ultimate goal of attaining an average
temperature of about 250.degree. F. a depth of at least 2 inches,
can often lead to scorching or overheating of the asphalt surface.
Unfortunately, attempts to obviate this effect simply by lowering
the temperature of the radiative surface, leads to even poorer
efficiencies in the overall recycling process and thus, is not
consideration a commercially viable alternative. A further problem
associated with conventional radiation heaters is the high
potential for non-uniform heating. Typically, this results from
certain areas in the asphalt surface attracting radiation (e.g. oil
spots) and other areas reflecting radiation (e.g. light coloured
aggregate). The problem is exasperated in areas of the asphalt
surface attracting radiation since this typically leads to severe
smoking and/or ignition of the asphalt surface thereby creating a
significant environmental concern.
As alluded to above, a conventional asphalt surface heater is a hot
air heater. Such a heater is described in U.S. Pat. No. 4,561,800
[Hatakenaka et al. (Hatakenaka)], the contents of which are hereby
incorporated by reference. Hatakenaka teaches a method of and an
apparatus for heating a road surface, in which hot air controlled
to a predetermined temperature is blown against the road surface so
as to heat the road surface. The apparatus includes a hot air
generator provided with a burner and a thermal control unit, and a
number of ducts formed with blowing pores for blowing the hot air
against the road surface. Hatakenaka purports that the apparatus
facilitates reducing the amount of smoke produced during heating of
the asphalt surface. A principal consideration in Hatakenaka is the
ability to control the temperature of the hot air. Thus, the
essence of Hatakenaka is the provision of hot air at a controlled
temperature which hot air is used as the means by which the road
surface is heated. Hatakenaka asserts that one of the advantages of
the invention is the ability to adjust the "thermal capability" of
the heater simply by adjusting the temperature of the hot air
itself. This underlies the notation that, for all intents and
purpose, Hatakenaka relates to an apparatus which provides
substantially all heat by convection.
One of the principal difficulties with hot air and convection
heaters generally, and the apparatus taught by Hatakenaka
specifically, used in asphalt surface recycling relates to the
inability to convey sufficient amounts of the hot air to the
asphalt surface to enable heat transfer to take place to the
desired temperature and depth in the asphalt surface. The principal
reason for this is the size and hot air throughput (e.g. cubic feet
per minute or "cfm") necessary to expose the asphalt surface to
sufficient heat for a sufficient period of time to heat the surface
at a commercially viable rate of speed (e.g. 10-30 feet/minute)
makes it impractical and/or prohibitively expensive to build a
commercially useful apparatus. The result of this is that, in the
asphalt surface recycling art, hot air and convection heaters are
not commercially viable when compared to radiation heaters.
It would be desirable to have a method and apparatus for heating an
asphalt surface which method and apparatus overcome or reduce at
least one of the above-identified disadvantages of the prior
art.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a novel method
for heating an asphalt surface which obviates or mitigates at least
one of the disadvantages of the prior art.
It is another object of the present invention to provide a novel
apparatus for heating an asphalt surface which obviates or
mitigates at least one of the disadvantages of the prior art.
Accordingly, in one of its aspects, the present invention provides
a process for heating an asphalt surface comprising the steps
of:
igniting in a burner a combustible mixture comprised of a fuel and
oxygen to produce a hot gas;
feeding the hot gas to an enclosure having a radiative face
disposed above the asphalt surface, the radiative face having a
plurality of apertures; and
selecting the dimension of the apertures such that the hot gas: (i)
heats the radiative face to provide radiation heat transfer to the
asphalt surface; and (ii) passes through the apertures to provide
convection heat transfer to the asphalt surface.
In another of its aspects, the present invention provides an
asphalt surface heating apparatus comprising a hot gas producing
burner and an enclosure comprising an inlet for receiving hot gas
from the burner and a radiative face having a plurality of
apertures, the apertures having a dimension such that the hot gas:
(i) heats the radiative face to provide radiation heat transfer to
the asphalt surface; and (ii) passes through the apertures to
provide convection heat transfer to the asphalt surface.
The present inventors have discovered that it is possible to
achieve substantially uniform, quick and efficient heating of an
asphalt surface by utilizing an asphalt surface heating apparatus
which is capable of a total heat transfer (Q.sub.TOTAL) made up of
both convection heat transfer (Q.sub.C) and radiation heat transfer
(Q.sub.R) as follows:
Preferably, Q.sub.C is from about 20% to about 80%, more preferably
from about 35% to about 65%, even more preferably from about 40% to
about 60%, most preferably from about 45% to about 55% of
Q.sub.TOTAL, with the remainder in each case being Q.sub.R.
For present purposes, Q.sub.C may be readily calculated empirically
according to the following equation:
wherein:
=the convection heat-transfer coefficient;
A=the total surface area of the heater;
T.sub.1 =the temperature of the hot gas; and
T.sub.2 =the temperature of the asphalt surface.
Further, Q.sub.R may be readily calculated empirically according to
the following equation:
wherein:
.epsilon.=the total emissivity of the radiative surface;
.sigma.=the proportionality (Stefan-Boltzmann) constant;
A=the total surface area of the heater;
T.sub.1 =the temperature of the radiative face of the enclosure;
and
T.sub.2 =the temperature of the asphalt surface.
These equations and the use thereof are within the purview of a
person skilled in the art and are discussed in more detail in HEAT
TRANSFER by J. P. Holman (7th Edition, 1992), the contents of which
are hereby incorporated by reference.
For example, a useful asphalt surface heating apparatus is
constructed has a radiative face constructed of oxidized steel and
is operated at approximately 1200.degree. F. The radiative face is
used approximately 3 inches off the asphalt surface. Radiative
surface is about 12 feet wide by 26 feet wide and is provide with a
total of approximately 15,500 circular apertures have a diameter of
0.25 inches. For such an apparatus, a person skilled in the art can
readily calculate that Q.sub.C is approximately 480 kW (48% of
total heat transfer) whereas Q.sub.R is approximately 520 kW (52%
of total heat transfer).
One of the principal advantages of the present asphalt surface
heating apparatus is that it is not dependent on the use of a
particular type of fuel. Thus, it is believed that the present
asphalt surface heating apparatus is the first such apparatus which
combines at least partial heat transfer by radiation with the
flexibility of using a liquid fuel such as diesel fuel.
Throughout this specification, reference is made to combustion a
mixture of fuel and oxygen. As is well known, pure oxygen is
extremely flammable and dangerous to handle and use. Thus, for most
applications, it is convenient to use ambient air for admixture
with the fuel. It should be clearly understood, however, that the
scope of the present invention includes the non-air gases
comprising or consisting of oxygen.
Preferably, the present asphalt surface heating apparatus further
comprises means to dispose the enclosure above the asphalt surface
at a distance of from about 1 to about 6, more preferably from
about 2 to about 4, most preferably from about 2 to about 3, inches
above the asphalt surface being heating. This serves to optimize
exposure of the asphalt surface to radiation emanating from the
radiative face of the enclosure.
Preferably, the enclosure in present asphalt surface heating
apparatus comprises a plurality of substantially adjacent tubes,
each of the tubes have a radiative face. It is particularly
preferred to dispose the tubes in a manner whereby a gap or spacing
is provided between adjacent pairs of tubes. The provision of such
a gap or tube facilitates recycling of the hot gas impacting the
asphalt surface. Specifically the hot gas may be drawn back to the
burner through the gap or spacing between adjacent pairs of tubes.
Ideally, the gap or spacing between adjacent pairs of tubes is of a
size such that the velocity of the hot gas being recycled is in the
range of from about 20% to about 80%, preferably from about 30% to
about 70%, more preferably from about 40% to about 60%, most
preferably from about 45% to about 55% of the velocity of the hot
gas passing through the apertures in the tubes.
The temperature of the hot gas and the radiative face of the
enclosure are approximately the same although this is not
essential. Preferably, this temperature is in the range of from
about 700.degree. to about 1600.degree. F., more preferably from
about 900.degree. to about 1400.degree. F., most preferably from
about 1000.degree. to about 1200.degree. F. Ideally the temperature
is about 1100.degree. F.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described with
reference to the accompanying drawings wherein like numerals depict
like parts and in which:
FIG. 1 illustrates a side elevation of a schematic of the present
asphalt surface heating apparatus;
FIG. 2 illustrates a bottom view of a portion of the apparatus
illustrated in FIG. 1; and
FIG. 3 illustrates a front elevation of the apparatus illustrated
in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to FIGS. 1-3, there is illustrated an asphalt
surface heating apparatus 10. Heating apparatus 10 is mobile and is
mounted on or attached to a suitable vehicle (not shown) mounted on
wheels 20 (illustrated in a ghosted fashion).
Heating apparatus 10 includes a housing 25 having a burner 30, the
outlet end of which is disposed in a combustion chamber 40. Burner
30 comprises a fuel inlet 50, an oxygen inlet 60 and a
mixing/atomization chamber 70. Burner 30 further comprises a nozzle
80 disposed in housing 25. As illustrated, the downstream end of
nozzle 80 is surrounded by the inlet of combustion chamber 40.
While it is possible to dispose the end of nozzle 80 in sealing
engagement with the inlet of combustion chamber 40, it is
particularly preferred to have a space between the end of nozzle 80
and combustion chamber 40.
Housing 25 is divided by a wall 100 into an exhaust gas housing 110
and a hot gas housing 120. As illustrated, combustion chamber 40
comprises a plurality of combustion apertures 90 disposed such that
they are in both exhaust gas housing 110 and hot gas housing 120.
Exhaust gas housing 110 is connected to an exhaust 130 equipped
with a damper 140. It is a preferred feature of combustion chamber
40 that size and number of apertures 90 is selected so as to result
in from about 5% to about 20%, more preferably from about 5% to
about 15%, most preferably from about 8% to about 10%, by volume of
the total volume of hot gas produced in combustion chamber 40 being
directed to exhaust gas housing 110 with remainder being directed
to hot gas housing 120. In practice, this results in the majority
of the aperture surface area (i.e. the total surface of apertures
90) being represented by apertures which are in hot gas housing
120.
Hot gas housing 120 comprises a hot gas recycle inlet 150 and a hot
gas outlet 160. Hot gas outlet 160 is connected to a plenum 170.
Plenum 170 comprises a hot gas supply chamber 180 which is
connected to a plurality of hot gas discharge enclosures 190. Hot
gas supply chamber 180 and hot gas discharge chambers each comprise
a radiative face 200. Each radiative face 200 comprises a plurality
of apertures 210. Hot gas discharge chambers 190 are arrange such
that there is provided a spacing 220 between adjacent pairs of
chambers.
Plenum 170 further comprises a recycle gas return chamber 230 which
is connected to a recirculation fan unit 240 having disposed
therein a blower (not shown). Recirculation fan unit 240 is
connected to housing 25 by a recycle gas supply chamber 250 having
damper 260 disposed therein.
In operation, fuel and oxygen are introduced into inlets 50 and 60,
respectively, of burner 30 wherein they are mixed and atomized (if
the fuel is a liquid at ambient temperature and pressure) in
chamber 70 to form a combustible mixture. The combustible mixture
is then passed to nozzle 80 wherein ignition occurs result in the
production of a flame 270 and hot gas. The hot gas generally moves
in the direction of arrow A whereby it exits combustion chamber 40
via apertures 90 in two streams. The majority of hot gas exits as
depicted by arrow B a minor amount of hot gas exits as depicted by
arrow C.
Hot gas depicted by arrow B enters plenum 170 through hot gas
outlet 160 wherein it is fed to hot gas supply chamber 180 and hot
gas discharge chambers 190. The hot gas then exits chambers 180 and
190 via apertures 210 in the radiative faces 200 of each chamber
180 and 190. By careful design of radiative faces 200 in chambers
180 and 190, and selection of the number and size of apertures 210,
radiative faces 200 facilitate both radiation and convection heat
transfer. Thus, the hot gas serves to heat radiative faces 200 to a
temperature at which they emit radiation, preferably infrared
radiation. Concurrently, hot gas passes through apertures 210 at
high velocity and impinges on an asphalt surface 280 to be heated
thereby be providing convection heat transfer.
Recirculation fan unit 240 serves to recycle gas depicted by arrows
D through spacings 220 between adjacent pairs of hot gas discharge
chambers 190. Recirculation fan unit 240 feeds the recycle gas to
recycle gas supply chamber 250 as depicted by arrow E. Recycle gas
entering housing 25 either (i) enters combustion chamber 40 as
depicted by arrow F wherein any partially- or non-combusted fuel is
fully burned; or (ii) flows around and heat exchanges with the
outside of combustion chamber 40 as depicted by arrows G after
which it is mixed with hot gas emanating from combustion chamber 40
as depicted by arrow B.
The present asphalt surface heating apparatus can be used to
advantage in virtually all hot-in-place recycling process include
those described in the United States patents referred to
hereinabove. However, the present asphalt surface heating apparatus
finds particular advantageous application when combined with the
process and apparatus described in each of copending Canadian
patent applications 2,061,682 and 2,102,090, and International
patent application WO93/17185, the contents of each of which are
hereby incorporated by reference.
Accordingly, while this invention has been described with reference
to illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications of the
illustrative embodiments as well as other embodiments of the
invention, will be apparent to persons skilled in the art upon
reference to this description. For example, it is possible to
construct the present asphalt surface heating apparatus such that
it provides radiation heat transfer and convection heat transfer in
sequential or, preferably, a cyclical and sequential manner. This
can be achieved in a number of ways such as the provision of tubes
arranged substantially transverse to the asphalt surface The tubes,
optionally having apertures, as described hereinabove and could
have disposed between them a conventional radiation heater.
Alternatively, it is possible to construction a train of apparatus
which alternates between a convection heater and a radiation
heater. The net result of this is an apparatus train which, in
total, transfers heat by radiation and convection. It is therefore
contemplated that the appended claims will cover any such
modifications or embodiments.
* * * * *